Dual inner diameter ferrule device and method

ABSTRACT

A fiber optic ferrule includes a body extending from a first end to a second opposite end, with the body including an axial passage extending between the first and second ends. The axial passage includes a first diameter portion having a diameter of at least 125 microns, and a second diameter portion having a diameter of at least 250 microns and less than a diameter of the buffer, the second diameter portion positioned between the first diameter and the second end. The axial passage further defines a tapered shape at the second end extending inward from the second end to the second diameter portion. A hub holds the ferrule. A method of assembling a terminated fiber optic cable is also provided.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 12/271,335,filed Nov. 14, 2008, which is a continuation of application Ser. No.11/972,373, filed Jan. 10, 2008, now U.S. Pat. No. 7,452,137, which is acontinuation of application Ser. No. 11/497,175, filed Aug. 1, 2006, nowU.S. Pat. No. 7,341,383, which applications are incorporated herein byreference in its entirety.

Field of the Invention

The present invention relates to terminating the ends of fiber opticcables with ferrules.

BACKGROUND OF THE INVENTION

Typically the end of a fiber optic cable is terminated by a fiber opticconnector by gluing the fiber within the cable to a ferrule of theconnector. A well known fiber optic cable size includes an inner glassfiber of 125 microns in diameter, with an outer coating of 250 micronsin diameter, covered by a polymeric buffer layer of 900 microns indiameter.

One problem with terminating fiber optic cables can include fiberbreakage at the rear interface area between the end of the glass fiberand the ferrule. In this interface area is the epoxy used to hold thefiber to the ferrule. Such breakage tends to increase in response togreater temperature fluctuations during use of the cables. Differencesin thermal expansion are believed to cause the breakage. There is a needto improve the interface between fiber optic cables and connectors toreduce fiber breakage, especially due to thermal stress.

SUMMARY OF THE INVENTION

A fiber optic ferrule includes a body extending from a first end to asecond opposite end, with the body including an axial passage extendingbetween the first and second ends. The axial passage includes a firstdiameter portion having a diameter of at least 125 microns, and a seconddiameter portion having a diameter of at least 250 microns, the seconddiameter portion positioned between the first diameter and the secondend. The axial passage further defines a funnel shape at the second endextending inward from the second end to the second diameter portion.

A method of assembling a terminated fiber optic cable includes providinga cable with an inner fiber at 125 microns, an outer coating at 250microns, and a buffer layer at 900 microns. The method includesstripping a portion of the coating from an end of the cable to expose aportion of the inner fiber, and stripping a portion of the buffer layerto expose a portion of the coating. The method further includesinserting the exposed fiber and the exposed coating into a ferrulehaving first and second inner diameters, wherein the first diameter isat least 125 microns, and the second diameter is at least 250 microns,and adhesively holding the fiber to the ferrule.

The present invention also relates to a device and method for mounting afiber to a ferrule wherein the ferrule includes a first passagewayportion sized only to receive a bare fiber without a coating or a bufferlayer, and a second passageway portion sized to receive the fiberincluding the coating, but no buffer layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view of one embodiment of a ferrule anda hub in accordance with the present invention;

FIG. 2 is an end view of the ferrule and hub of FIG. 1;

FIG. 3 is a cross-sectional side view of the ferrule of FIG. 1;

FIG. 4 is a cross-sectional side view of the ferrule and hub of FIG. 1,and including a fiber optic cable inserted into the inner passagethrough the ferrule;

FIG. 5 is an enlarged cross-sectional view of a portion of the ferrule,hub, and cable of FIG. 4;

FIG. 6 is a cross-sectional side view of the ferrule and hub of FIG. 1,and including a fiber optic cable inserted into the inner passagethrough the ferrule, with the fiber coating layer not as fully insertedinto the ferrule;

FIG. 7 is an enlarged cross-sectional view of a portion of the ferrule,hub, and cable of FIG. 6;

FIG. 8 is a cross-sectional side view of a prior art ferrule and hub.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIGS. 1-7, a preferred embodiment is a fiber opticferrule 10 is shown mounted to a hub 12. Generally, ferrule 10 and hub12 are secured together by convenient methods including press fit oradhesive mounts. Ferrule 10 and hub 12 are mounted within a connectorhousing 13 shown in dashed lines in FIG. 1. Connector housing 13 can beone of a variety of well known connector types, including SC, FC, ST,LX.5, LC, and others. As will be described below, ferrule 10 and hub 12are connected to an end of a fiber optic cable for use in connectorizingthe end of the cable.

Ferrule 10 includes a body 16 with a first end 20 defining a ferruletip. Body 16 of ferrule 10 includes an opposite end 24 received in apocket 14 of hub 12. Ferrule 10 includes a central axis 28. First end 20of ferrule 10 is typically polished along with the fiber after the fiberis installed. Body 16 of ferrule 10 is typically ceramic inconstruction.

Ferrule 10 includes a central passage 30 concentric with axis 28.Central passage 30 extends from first end 20 to opposite end 24. Centralpassage 30 includes a first portion 34 having a first diameter, anintermediate or second portion 38 having a second diameter, and a rearor third portion 42. First portion 34 is sized to receive the innerfiber sized at 125 microns. Second portion 38 is sized to receive theportion of the cable including the outer coating at 250 microns. Thirdportion 42 is tapered inward from opposite end 24 so as to facilitateinsertion of the fiber during installation.

In prior art ferrules, such as ferrule 100 shown in FIG. 8, dualdiameters were not provided. In particular, the ferrule 100 of FIG. 8includes a central passage 130 having a uniform diameter sized forreceipt of the inner fiber at 125 microns. A tapered portion 132 extendsfrom end 134 to central passage 130.

In contrast, ferrule 10 includes dual diameter portions 34, 38, eachspecially sized to receive the inner fiber (125 microns) and a portionof the outer coating (250 microns), respectively.

Referring now to FIGS. 4 and 5, a fiber optic cable 50 is shown with aninner fiber 52, an outer coating 54, and a buffer layer 56. Fiber 52terminates at end 53. Typically, end 53 is removed and polished with end20 of ferrule 10. Coating 54 terminates at end 55. Buffer layer 56terminates at end 57. As shown, a portion of coating 54 extends beyondend 57 of buffer layer 56.

With special reference to FIG. 5, ferrule 10 closely surrounds fiber 52,and coating 54. Epoxy is used within central passage 30 to adhesivelyhold cable 50 to ferrule 10. However, very little epoxy is positionedaround end 55 of coating 54. By reducing the volume of epoxy positionedaround end 55 of coating 54, less thermally induced stresses are appliedto fiber 52. As shown, passage 30 defines a small conically shapedpocket 59 around end 55 of coating 54. Pocket 59 is the transition areabetween first and second portions 34, 38 of central passage 30. Byallowing coating 54 to extend past end 57 of buffer layer 56, and thenbe received in pocket 59, a smaller amount of epoxy is in contact withfiber 52 adjacent end 55 of coating 54. Less epoxy around the interfacebetween coating 54 and fiber 52 will reduce the thermal effects causedby any differences in thermal expansion between fiber 52 and the epoxy.

Coating 54 does not need to be fully inserted into ferrule 10, as shownin FIGS. 4 and 5. As shown in FIGS. 6 and 7, pocket 59 is larger aroundthe end 55 of coating 54. Such an arrangement still provides less epoxyaround fiber 52, than in the arrangement of FIG. 8. One example epoxy isF123 from Tra-con, Inc. of Bedford, Mass.

In ferrule 10, first portion 34 has a first dimension sized large enoughto receive the uncoated fiber, but not so large as to receive the coatedfiber. Second portion 38 has a second dimension large enough to receivethe coated fiber, but not so large as to receive the buffer.

In the illustrated embodiment, first portion 34 is cylindrically shapedand sized at 0.1255 mm+/−0.0015/0.0000 mm to receive the inner fibersized at 125 microns. Second portion 38 is cylindrically shaped andsized at 0.260 mm+/−0.010 mm to receive the portion of the cableincluding the outer coating at 250 microns. A preferred range for secondportion 38 is greater than 250 microns, and less than or equal to 500microns.

A more preferred range for second portion 38 is greater than 250microns, and less than or equal to 300 microns. In the illustratedembodiment, ferrule 10 is 10.5 mm long, with second portion 38 extendinginto ferrule 10 about 3 mm from end 24.

The above specification, examples and data provide a completedescription of the manufacture and use of the composition of theinvention. Since many embodiments of the invention can be made withoutdeparting from the spirit and scope of the invention, the inventionresides in the claims hereinafter appended.

1. A fiber optic ferrule and cable comprising: a ferrule body extending from a first end to an opposite second end, the ferrule body having an outer cylindrical shape, the ferrule body including an axial passage extending between the first and the second ends of the ferrule body, the axial passage of the ferrule body including: a first diameter portion generally cylindrical in shape adjacent the first end of the ferrule body; a second diameter portion generally cylindrical in shape positioned between the first diameter portion and the second end of the ferrule body; and a transition area between the first and the second diameter portions; an optical fiber cable including an inner fiber, an outer coating, and a buffer layer, the outer coating positioned around the inner fiber and the buffer layer positioned around the outer coating, a portion of the outer coating and inner fiber extending beyond an end of the buffer layer and a portion of the inner fiber extending beyond an end of the outer coating; a hub mounted around the second end of the ferrule body, the hub including an axial passage; and an adhesive material within the axial passage of the ferrule body holding the optical fiber cable to the ferrule body; wherein the first diameter portion of the axial passage of the ferrule body receives the inner fiber of the optical fiber cable; wherein the second diameter portion of the axial passage of the ferrule body receives the outer coating of the optical fiber cable; wherein the end of the buffer layer of the optical fiber cable is positioned in the axial passage of the hub; and wherein the outer coating of the optical fiber cable is spaced from the transition area between the first and the second diameter portions of the axial passage of the ferrule body.
 2. The fiber optic ferrule and cable of claim 1, wherein the transition area is conically shaped. 3-6. (canceled)
 7. The fiber optic ferrule and cable of claim 1, wherein the adhesive material is an epoxy. 8-9. (canceled)
 10. The fiber optic ferrule and cable of claim 1, wherein the ferrule body is a ceramic ferrule body. 11-14. (canceled)
 15. The fiber optic ferrule and cable of claim 1, wherein the first diameter portion of the axial passage of the ferrule body has a diameter of at least 125.5 microns and less than or equal to 127 microns. 16-17. (canceled)
 18. The fiber optic ferrule and cable of claim 1, wherein the second diameter portion of the axial passage of the ferrule body has a diameter of greater than 250 microns and less than or equal to 300 microns. 19-21. (canceled)
 22. A method of assembling a ferrule terminated cable comprising: providing a cable with an inner fiber, an outer coating around the inner fiber, and a buffer layer around the outer coating; stripping a portion of the buffer layer from an end of the cable to expose a portion of the outer coating; stripping a portion of the exposed outer coating from the end of the cable to expose a portion of the inner fiber, thereby creating a new end of the exposed outer coating; inserting the exposed portion of the inner fiber and the remaining exposed portion of the outer coating into an axial passage of a ferrule body having an outer cylindrical shape, the axial passage of the ferrule body having first and second inner diameters and a transition area between the first and the second inner diameters, wherein the first inner diameter only receives the inner fiber and no outer coating and the second inner diameter receives at least a portion of the outer coating and no buffer layer, wherein the ferrule body is mounted to a hub adjacent to an end of the ferrule body, the hub including an axial passage, wherein an end of the buffer layer is positioned in the axial passage of the hub, and wherein the new end of the exposed outer coating of the cable is spaced from the transition area; and adhesively holding the cable to the ferrule body.
 23. The method of claim 22, wherein the transition area between the first and the second inner diameters of the axial passage of the ferrule body is conically shaped. 24-26. (canceled)
 27. The method of claim 22, wherein epoxy is used within the axial passage of the ferrule body to adhesively hold the exposed portion of the inner fiber to the axial passage. 